1. Field of the Invention
The present invention relates to equipment for assessing the functional peripheral visual field.
2. Description of the Related Art
Visual field testing belongs to the subspecialty of ophthalmology. However, it is very often performed at the primary health care level too, for example, as part of the medical examination required for obtaining a driver's license. The importance of visual field testing is emphasized by the Jul. 1, 1996, EU directive concerning health standards for drivers, which mandates "a field of vision of at least 120 degrees in the horizontal plane" as part of the minimum visual requirements for safe driving.
Many types of technical equipment have been developed for ophthalmologists working in hospitals and outpatient clinics. Nowadays the majority are computerized. The relevant literature (R. D. Harley, Pediatric Ophthalmology, 2.sup.nd edition, p. 127, FIG. 4-32) contains only one mention of a method in which the examiner stands behind the examinee. All other methods position the examiner in front of the examinee or to the side. Perimetry examinations focus mainly on the diagnosis of diseases and on the determination of the central visual field during monocular examination. Functional binocular visual field testing has not yet been accepted into general practice, nor has its importance been emphasized. Furthermore, binocular examination has involved very complicated methods not easily utilized at the primary care level.
At this moment all physicians can choose from a variety of finger perimetry techniques for visual field testing. In the traditional static finger confrontation method, which is shown FIG. 1, the doctor D sits facing the examinee E at a distance of one meter and introduces fingers into the examinee's visual field from the periphery with the arms outstretched to the sides. While maintaining focus on the tip of the doctor's nose, the examinee tells how many fingers the doctor is holding up on either hand. In the kinetic confrontation method, the doctor and examinee are positioned as above, with the examinee again gazing at the tip of the doctor's nose. The doctor moves his hands from the periphery towards the center field, and the examinee signals when he/she can see the moving fingers. Results are compared with the doctor's own perception, and the techniques are poorly standardized.
This examiner has encountered many problems assessing visual fields during his 15 years of general practice, and many of his colleagues have expressed similar dissatisfaction with finger perimetry techniques. First, visual field defects are rare among people younger than 60 years of age, and those defects induced by glaucoma in older people are very difficult to verify by finger perimetry, so there are "never" positive findings. Also, because assessment of the visual fields by finger perimetry depends on cooperation between the doctor and the examinee as well as on the method, the examiner is plagued by uncertainty. This uncertainty arises because: (a) the examinee can see the position of the examiner's arms throughout the examination, (b) the extent of the field tested is limited by the examiner's armspan, (c) results can be recorded only as "normal" or "abnormal", not in degrees (as required by the EU directive on drivers' health standards), (d) the "wiggling fingers and moving arms" method appears rather comical, and does not increase the examinees' motivation or understanding, and (e) size differences between the examiner and examinee lead to further difficulties (for example, in the examination of children).